Memory cells and methods of forming memory cells

ABSTRACT

Some embodiments include a method of forming a memory cell. A first portion of a switching region is formed over a first electrode. A second portion of the switching region is formed over the first portion using atomic layer deposition. The second portion is a different composition than the first portion. An ion source region is formed over the switching region. A second electrode is formed over the ion source region. Some embodiments include a memory cell having a switching region between a pair of electrodes. The switching region is configured to be reversibly transitioned between a low resistive state and a high resistive state. The switching region includes two or more discrete portions, with one of the portions not having a non-oxygen component in common with any composition directly against it in the high resistive state.

RELATED PATENT DATA

This patent resulted from a continuation of U.S. patent application Ser.No. 15/334,186 which was filed Oct. 25, 2016, which is a divisional ofU.S. patent application Ser. No. 14/584,504 which was filed Dec. 29,2014, which resulted from a divisional of U.S. patent application Ser.No. 13/738,201 which was filed on Jan. 10, 2013, now U.S. Pat. No.8,921,821; each of which is hereby incorporated by reference.

TECHNICAL FIELD

Memory cells and methods of forming memory cells.

BACKGROUND

Integrated memory may be used in computer systems for storing data.Integrated memory is usually fabricated in one or more arrays ofindividual memory cells. The memory cells are configured to retain orstore memory in at least two different selectable states. In a binarysystem, the states are considered as either a “0” or a “1”. In othersystems, at least some individual memory cells may be configured tostore more than two levels or states of information.

An example memory cell is a programmable metallization cell (PMC). Suchmay be alternatively referred to as conductive bridging random accessmemory (CBRAM), nanobridge memory, or electrolyte memory. A PMC may useion conductive switching material (for instance, a suitable chalcogenideor any of various suitable oxides) and an ion source material adjacentthe switching material. The ion source material and switching materialmay be provided between a pair of electrodes. A suitable voltage appliedacross the electrodes can cause ions to migrate from the ion sourcematerial into the switching material to thereby create one morecurrent-conductive paths through the switching material. An oppositevoltage applied across the electrodes essentially reverses the processand thus removes the current-conductive paths. A PMC thus comprises ahigh resistance state (corresponding to the state lacking a conductivebridge extending through a switching material) and a low resistancestate (corresponding to the state having a conductive bridge extendingthrough a switching material), with such states being reversiblyinterchangeable with one another.

Although there has been effort toward development of PMCs and othermemory cells, there remains a need for improved memory cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatically illustrates an example embodiment PMC reversiblytransitioning between a low resistance state and a high resistancestate.

FIGS. 2-4 show a semiconductor construction in cross-sectional view, anddiagrammatically illustrate process stages of an example embodimentprocess for forming an example embodiment memory cell.

FIGS. 5-7 show a semiconductor construction in cross-sectional view, anddiagrammatically illustrate process stages of another example embodimentprocess for forming another example embodiment memory cell.

FIGS. 8 and 9 show a semiconductor construction in cross-sectional view,and diagrammatically illustrate process stages of another exampleembodiment process for forming another example embodiment memory cell.

FIG. 10 diagrammatically illustrates another example embodiment memorycell.

FIG. 11 diagrammatically illustrates another example embodiment memorycell.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Two performance aspects of PMCs are switching and retention. It isdesired that switching be relatively easy so that a PMC may be rapidlyswitched from one memory state to another with relatively low voltage.It is also desired that a PMC have good retention characteristics, sothat the PMC does not inadvertently switch between memory states withoutthe appropriate voltage input. Characteristics which lead to easyswitching are often opposite to those which lead to good retention. Adifficulty encountered in fabrication of PMCs is that it can bedifficult to balance the competing goals of easy switching and goodretention. Some embodiments provided herein utilize two or moredifferent compositions within a switching region to enablecharacteristics of the switching region to be tailored to achieve adesired balance between switchability and retention. Example embodimentsare described with reference to FIGS. 1-11.

Referring to FIG. 1, a PMC 10 is illustrated in two modes correspondingto a high resistance state (HRS) and a low resistance state (LRS). Thetwo modes are reversibly interchanged with one another throughapplication of electric fields EF⁺ and EF⁻, with EF⁺ being of oppositepolarity relative to EF⁻.

The PMC device comprises a pair of electrodes 12 and 14; and comprises aswitching region 16 and an ion source region 18 between the electrodes.

Electrodes 12 and 14 may comprise any suitable electrically conductivecomposition or combination of compositions; and may be the samecomposition as one another or may be different compositions relative toone another. In some embodiments, the electrodes may comprise, consistessentially of, or consist of one or more of various metals (forexample, tungsten, titanium, etc.), metal-containing compositions (forinstance, metal nitride, metal carbide, metal silicide, etc.), andconductively-doped semiconductor materials (for instance,conductively-doped silicon, conductively-doped germanium, etc.). Forinstance, in some embodiments the electrode 12 may comprise, consistessentially of, or consist of titanium nitride; and the electrode 14 maycomprise, consist essentially of, or consist of tungsten.

In the shown embodiment, the electrode 12 extends through a dielectricmaterial 13. In some embodiments, such dielectric material may comprise,consist essentially of, or consist of silicon nitride.

The memory cell 10 is shown to have the bottom electrode 12 connected toexternal circuitry 30, and to have the top electrode 14 connected toexternal circuitry 32. Circuitries 30 and 32 may include sense and/oraccess lines coupled to the electrodes, and configured for providingappropriate electric fields across the memory cell during read/writeoperations. In some embodiments, the illustrated memory cell may be oneof a plurality of memory cells of a memory array, and the circuitries 30and 32 may be part of a circuit configuration utilized to uniquelyaddress each of the memory cells of the array. In some embodiments, a“select device” (not shown) may be provided adjacent the memory cell 10to reduce undesired current leakage to and/or from the memory cellduring utilization of the memory cell in a memory array. Example selectdevices include diodes, transistors, ovonic threshold switches, etc.

The ion source region 18 contributes ions which ultimately form one ormore conductive bridges across the switching region 16. The ion sourceregion may comprise any suitable composition or combination ofcompositions. In some embodiments, the ion source region may compriseone or more of aluminum, copper, silver and tellurium; and may beconfigured for contributing aluminum cations, copper cations and/orsilver cations for formation of one or more conductive bridges.

Although the ion source region is shown comprising a single composition,in other embodiments the ion source region may comprise two or moredifferent compositions. For instance, in some embodiments the ion sourceregion may have a first portion comprising AlTeN, where the listedcomposition is described in terms of elemental constituents rather thanin terms of a specific stoichiometry; and may have a second portioncomprising CuZrAlTeO, where the listed composition is described in termsof elemental constituents rather than in terms of a specificstoichiometry. The first portion may be directly against the switchingregion 16, and the second portion may be between the first portion andthe top electrode 14. An ion source region comprising two portions isdescribed below with reference to FIG. 4.

At least a portion of the switching region 16 may be formed by atomiclayer deposition (ALD) to enable such portion to be tailored relative tocomposition and thickness. For instance, the illustrated switchingregion 16 of FIG. 1 is shown to comprise two portions 20 and 22 ofdifferent compositions relative to one another, with an interfacebetween such two portions being diagrammatically illustrated with theline 19; and in some embodiments at least one of such portions may beformed with ALD.

In some embodiments, a switching region portion formed by ALD may have athickness within a range of from greater than 0 angstroms (Å) to lessthan or equal to about 20 Å; and in some embodiments may have athickness of less than or equal to about 12 Å. In the shown applicationof FIG. 1 in which the switching region comprises two portions 20 and22, both of such portions may be formed by ALD in some embodiments; andin other embodiments one of the portions may be formed by ALD, and theother portion may be formed by any other suitable method, including, forexample, physical vapor deposition (PVD), chemical vapor deposition(CVD), and/or oxidation of a surface underlying such portion. Forinstance, in some embodiments the portion 20 may be formed by oxidationof a surface of electrode 12, and thus may comprise titanium oxide orTiO_(x)N_(y) in embodiments in which electrode 12 comprises titaniumnitride. If the portion 20 is formed by oxidation of a surface ofelectrode 12, the portion 20 may extend only across the upper surface ofelectrode 12, rather than having the shown configuration in which theportion 20 also extends across surfaces of dielectric material 13.

The various portions of the switching region may comprise any suitablecomposition or combination of compositions; and in some embodiments maycomprise, consist essentially of, or consist of one or more of GeS,GeSe, SiO, ZrO, TiO, TaO, HfO, AlO, WO, SnO, NbO, HfSiO, ZrTiO, ZrWO,AlTiO, VO, MoO, NiO, YO, ReO, MnO, FeO, SiAlO, SiTiO, etc.; where thelisted compositions are described in terms of elemental constituents,rather than in terms of specific stoichiometries (for instance, AlO maycorrespond to Al₂O₃). In some embodiments, an ALD-formed portion maycomprise HfSiO formed to a thickness within a range of from greater than0 angstroms to less than or equal to about 16 angstroms; and in someembodiments a total thickness of a two-portion switching region may beabout 20 angstroms, with one of the portions being ALD-formed HfSiOhaving a thickness of about 16 angstroms.

In some embodiments, one of the portions 20 and 22 may consist of oxygenin combination with one or more transition metals (specifically, metalswithin groups 3-12 of the periodic table); and the other of the portions20 and 22 may consist of oxygen in combination with one or morenon-transition elements (i.e., elements not within groups 3-12 of theperiodic table); where the non-transition elements may be selected fromthe group consisting of metals, semi-metals, alkaline earth elements,and mixtures thereof in some embodiments. For instance, in someembodiments one of the portions may comprise one or more of hafniumoxide, zirconium oxide and titanium oxide; and the other of the portionsmay comprise one or both of silicon dioxide and aluminum oxide. In anexample embodiment utilizing an alkaline earth element, one of theportions may comprise magnesium oxide. Either or both of the portionsmay be formed by ALD, and either or both of the portions may have athickness within a range of from greater than 0 Å to less than or equalto about 20 Å, and in some embodiments less than or equal to about 12 Å.

The utilization of two portions of different compositions relative toone another in the switching region 16 can enable characteristics of theswitching region to be tailored to achieve a desired balance betweenswitchability and retention. In some embodiments it is found that theutilization of an ALD-formed portion of the switching region can enablethe switching region to be formed with characteristics better than thoseachieved in the absence of such ALD-formed portion. For instance, insome embodiments one of the first and second portions of the switchingregion comprises hafnium oxide and the other comprises aluminum oxide;with at least one of the portions being formed by ALD. The switchingregion is found to have better switchability and retentioncharacteristics relative to a switching region comprising only hafniumoxide, or only aluminum oxide. Further, the balance betweenswitchability and retention may be correlated to the relativethicknesses of the hafnium oxide and the aluminum oxide, and thus suchbalance may be tuned utilizing adjustments of the relative thicknesses.

Although the switching region of FIG. 1 comprises two portions, in otherembodiments switching regions may be formed to comprise more than tworegions. An example of a switching region comprising more than tworegions is described below with reference to FIG. 10. Also, in someembodiments a switching region may be formed to comprise a singlehomogeneous ALD-formed material, rather than multiple portions. Anexample of a switching region comprising only a single homogeneousALD-formed material is described below with reference to FIG. 11.

In some embodiments, an ALD-formed portion of a switching region mayhave a thickness less than a single monolayer; or in other words may beformed with too few cycles to complete a full monolayer. For instance,in some embodiments an ALD-formed portion may be formed utilizing fromone to five ALD cycles under conditions which fail to complete a fullmonolayer, and thus may comprise modified regions scattered across asurface. An example embodiment in which a portion of a switching regionis formed to comprise scattered modified regions, rather than a fullmonolayer, is described below with reference to FIGS. 8 and 9.

The switching region 16 of FIG. 1 is shown to comprise a conductivebridge 26 in the LRS mode, and to not comprise such conductive bridge inthe HRS mode. Although only one conductive bridge is shown, in someembodiments there may be multiple conductive bridges present in the LRSmode. Also, although the conductive bridge 26 is shown to span an entiredistance from a top surface of electrode 12 to a bottom surface of ionsource 18, in other embodiments the conductive bridge may only extendpartially across such distance. For instance, in some embodiments aconductive bridge may be discontinuous, and may be broken by one or moresmall gaps. In operation, charge carriers may “jump” such gaps tocomplete a circuit across the switching region. Although the conductivebridge 26 is shown to be entirely absent in the HRS mode of the cell, inother embodiments a portion of the conductive bridge may be present inthe HRS mode.

Some example methods for forming example embodiment memory cells aredescribed with reference to FIGS. 2-9; with FIGS. 2-4 illustrating oneexample method, FIGS. 5-7 illustrating another example method, and FIGS.8 and 9 illustrating yet another example method.

Referring to FIG. 2, a construction 10 a comprises the electrode 12 andthe dielectric material 13 discussed above with reference to FIG. 1. Thefirst portion 20 of switching region 16 is formed over electrode 12, andin the shown embodiment is directly against an upper surface of theelectrode. The first portion 20 may be formed with any suitableprocessing, and in some example embodiments may be formed with one ormore of ALD, CVD, PVD and oxidation of an upper surface of electrode 12.

Referring to FIG. 3, the second portion 22 of the switching region isformed over the first portion 20 utilizing ALD. The switching region 16has a total thickness “T”, and in some embodiments such thickness may bewithin a range of from about 6 Å to about 20 Å. In some embodiments, theALD-formed portion 22 may have a thickness of from greater than 0 Å toless than or equal to about 12 Å. Thus, the ALD-formed portion 22 maycomprise at least about 50% of the total thickness of the switchingregion 16, by volume, in some embodiments; and may comprise less thanabout 50% of the total thickness, by volume, in other embodiments.

The first and second portions 20 and 22 are separate discrete portionsof the switching region 16, and thus comprise different compositionsrelative to one another. In some embodiments, one of the portions 20 and22 comprises a transition metal oxide, and the other does not. Forinstance, in some embodiments the portion 20 may comprise, consistessentially of, or consist of one or more transition metals incombination with oxygen; and the ALD-formed portion 22 may comprise,consist essentially of, or consist of one or more non-transitionelements in combination with oxygen; where at least one of thenon-transition elements may be selected from the group consisting ofmetals, semi-metals, alkaline earth elements, and mixtures thereof. Inother embodiments, the first portion 20 may comprise, consistessentially of, or consist of the one or more non-transition elements incombination with oxygen; and the second portion 22 may comprise, consistessentially of, or consist of the one or more transition metals incombination with oxygen. In some embodiments, the non-transitionelements may include one or both of silicon and aluminum, and thetransition metals may include one or more of hafnium, titanium andzirconium. Accordingly, in some embodiments the ALD-formed portion 22and the portion 20 may comprise different compositions from one another,with such composition comprising oxygen in combination with one or moreof aluminum, hafnium, silicon, titanium and zirconium.

In embodiments in which the ALD-formed portion 22 comprises transitionmetal oxide, the ALD formation of portion 22 may be considered tocomprise deposition of one or more transition metals over the surface ofportion 20; and in embodiments in which the ALD-formed portion 22comprises a non-transition element oxide, the ALD formation of portion22 may be considered to comprise deposition of one or morenon-transition elements over the surface of portion 20 (with suchnon-transition elements being selected from the group consisting ofmetals, semimetals, alkaline earth elements, and mixtures thereof, insome embodiments).

Referring to FIG. 4, an ion source region 18 is formed over switchingregion 16, and the top electrode 14 is formed over the ion sourceregion. In the shown embodiment, the ion source region 18 comprises twodiscrete portions 40 and 42, which may be referred to as a first portionand a second portion, respectively. In some embodiments, each of theportions 40 and 42 comprises at least one of copper, silver andaluminum. For instance, in some embodiments the first portion 40comprises AlTeN, where the listed composition is described in terms ofelemental constituents rather than in terms of a specific stoichiometry;and the second portion 42 comprises CuZrAlTeO, where the listedcomposition is described in terms of elemental constituents rather thanin terms of a specific stoichiometry. The first portion is directlyagainst the switching region 16 in the shown embodiment, and the secondportion is between the first portion and the top electrode 14.

The construction of FIG. 4 comprises a multi-portion switching region16. Such switching region may be tailored for particular applications byadjusting the thicknesses and compositions of the portions 20 and 22,which can provided advantages relative to prior art constructionsutilizing only a single material throughout a switching region. Aconstruction having a multi-portion switching region has been describedin the prior art, and specifically is described in U.S. PatentPublication 2011/0194329. Such construction forms one portion of amulti-portion switching region by oxidizing a surface, and thus acomposition of such portion of the multi-portion switching region isdictated by the surface underlying the switching region. In contrast,each portion of the multi-portion switching region 16 of FIG. 4 may beformed by a deposition process. Accordingly, whereas at least one of theportions of the switching regions of the constructions described in U.S.Patent Publication 2011/0194329 will have a non-oxygen component incommon with a composition directly against such portion, thecompositions of both portions of the switching region 16 of FIG. 4 mayhave compositions which do not have any non-oxygen component in commonwith compositions directly against such portions. In some embodiments,the relationship that both portions of the switching region 16 may havecompositions which do not have any non-oxygen component in common withcompositions directly against such portions holds true in the HRS modeof the memory cell (i.e., the mode in which a conductive filament doesnot extend through the switching material), but may not hold true in theLRS mode of the memory cell since the conductive filament may be formedof ions which migrate from a composition directly against the switchingmaterial. However, in some embodiments each portion of the switchingregion 16 may be considered to comprise a primary matrix within whichions migrate during assembly and disassembly of a conductive filament;and in such embodiments the primary matrix of each portion may be formedto not have any non-oxygen component in common with any compositiondirectly against such primary matrix regardless of whether the memorycell is in the HRS mode or the LRS mode.

The ability to utilize compositions of the switching material which donot have any non-oxygen components in common with compositions directlyagainst the switching material may enable the construction of FIG. 4 tobe formed with additional degrees of freedom relative to embodimentsdescribed in U.S. Patent Publication 2011/0194329, which may enable theconstruction of FIG. 4 to be better tailored for some applications.

Although it may be advantageous to form a switching material of acomposition which does not have any non-oxygen components in common withstructures directly against the switching material in some embodiments,in other embodiments it may be desired to form the switching material ofa composition having one or more non-oxygen components in common withthe structures directly against the switching material. Accordingly,some embodiments include formation of switching material having aportion containing one or more non-oxygen components in common withstructures directly against such portion of the switching material. Insuch embodiments, the portion of the switching material may be formedby, for example, ALD, CVD, PVD, and/or oxidation of a structure directlyagainst such portion of the switching material.

Although the embodiment of FIGS. 2-4 is described as having a firstportion 20 which may or may not be formed by ALD, and a second portion22 which is an ALD-formed portion; in other embodiments the processingmay be reversed so that the first portion 20 is an ALD-formed portion,and the second portion 22 may or may not be formed by ALD. FIGS. 5-7illustrate an example embodiment in which the first portion 20 is anALD-formed portion.

Referring to FIG. 5, a construction 10 b comprises the electrode 12 andthe dielectric material 13 discussed above with reference to FIG. 1. Thefirst portion 20 of switching region 16 is formed over electrode 12, andin the shown embodiment is directly against an upper surface of theelectrode 12. The first portion 20 may be formed with ALD, and in someembodiments may be formed to a thickness within a range of from greaterthan 0 Å to less or equal to about 12 Å.

Referring to FIG. 6, the second portion 22 of the switching region isformed over the first portion 20 utilizing, for example, one or more ofALD, CVD and PCD. The switching region 16 has the total thickness “T”,which in some embodiments may be within the range of from about 6 Å toabout 20 Å. In some embodiments, the ALD-formed portion 20 may compriseat least about 50% of the total thickness of the switching region 16, byvolume; in other embodiments may comprise less than about 50% of thetotal thickness, by volume; and in some embodiments may comprise about50% of the total thickness, by volume.

The first and second portions 20 and 22 are separate discrete portionsof the switching region 16, and may comprise the compositions discussedabove with reference to FIG. 3. Thus, in some embodiments one of theportions 20 and 22 of FIG. 6 comprises a transition metal oxide, and theother does not. For instance, in some embodiments the ALD-formed portion20 may comprise, consist essentially of, or consist of one or moretransition metals in combination with oxygen; and the portion 22 maycomprise, consist essentially of, or consist of one or morenon-transition elements in combination with oxygen; where at least oneof the non-transition elements may be selected from the group consistingof metals, semi-metals, alkaline earth elements, and mixtures thereof.In other embodiments, the ALD-formed portion 20 may comprise, consistessentially of, or consist of the one or more non-transition elements incombination with oxygen; and the second portion 22 may comprise, consistessentially of, or consist of the one or more transition metals incombination with oxygen. In some embodiments, both layers may consist ofone or more transition metal oxides (for example, hafnium oxide,tantalum oxide, etc.). In some embodiments, one or both of the layersmay comprise one or more metal nitrides (such as aluminum nitride), andin such embodiments the metal nitrides may be insulating metal nitrides.

Referring to FIG. 7, the ion source region 18 is formed over switchingregion 16, and the top electrode 14 is formed over the ion sourceregion. In the shown embodiment, the ion source region 18 comprises asingle homogeneous composition, but in other embodiments it may comprisetwo or more separate discrete portions (such as, for example, theportions 40 and 42 described above with reference to FIG. 4). In someembodiments, the ion source region 18 comprises at least one of copper,silver and aluminum; and may also comprise tellurium.

As mentioned above with reference to FIG. 1, some embodiments mayinclude ALD-formation of a portion of a switching region to a thicknessof less than about one monolayer. FIGS. 8 and 9 illustrate an example ofsuch embodiments.

Referring to FIG. 8, a construction 10 c comprises the electrode 12 andthe dielectric material 13 discussed above with reference to FIG. 1. Thefirst portion 20 of switching region 16 is formed over electrode 12, andin the shown embodiment is directly against an upper surface of theelectrode 12. The first portion 20 may be formed with any suitableprocessing, and in some example embodiments may be formed utilizing oneor more of ALD, CVD, PVD and oxidation of a surface of electrode 12.

A second portion of the switching region is formed over the firstportion 20 utilizing ALD, and in the shown embodiment the second portioncomprises scattered modified regions 50 formed across a surface ofportion 20. The modified regions 50 may be formed utilizing transitionmetal-containing precursor in some embodiments, and accordingly maycomprise one or more transition metals. Alternatively, or additionally,the modified regions 50 may be formed utilizing non-transitionelement-containing precursor, and accordingly may comprise one or morenon-transition elements. In some embodiments, such non-transitionelements may be selected from the group consisting of metals,semi-metals, alkaline earth elements, and mixtures thereof; andaccordingly may, for example, comprise one or both of aluminum andsilicon.

The modified regions 50 may be formed by utilizing too few ALD cycles toform a complete monolayer; and in some embodiments may be formedutilizing from one to five ALD cycles.

Referring to FIG. 9, the ion source region 18 is formed over switchingregion 16, and the top electrode 14 is formed over the ion sourceregion. In the shown embodiment, the ion source region 18 comprises asingle homogeneous composition, but in other embodiments it may comprisetwo or more separate discrete portions (such as, for example, theportions 40 and 42 described above with reference to FIG. 4). In someembodiments, the ion source region 18 comprises at least one of copper,silver and aluminum; and may also comprise tellurium.

The embodiments of FIGS. 1-7 utilize switching regions comprising twodiscrete portions. In other embodiments, switching regions may comprisemore than two discrete portions. For instance, FIG. 10 shows aconstruction 10 d illustrating an example embodiment memory cell havinga switching region 16 comprising a third portion 52 over the secondportion 22. In some embodiments, all of the portions 20, 22 and 52 maybe formed utilizing ALD. In other embodiments, one or more of theportions is formed utilizing processing other than ALD, but at least oneof the portions is formed utilizing ALD to enable careful tailoring ofthe composition and thickness of such portion. The multiple discreteportions of FIGS. 1-10 may remain in a finished construction in someembodiments, and in other embodiments a construction may be heated orotherwise treated to merge at least some of the portions into a combinedcomposition (such as, for example, an alloyed composition). Forinstance, in some embodiments alternating hafnium oxide layers andsilicon oxide layers may be formed as the discrete portions through ALD(or other suitable deposition, such as CVD or PVD), and such layers maybe subsequently treated to form hafnium silicate throughout theswitching region. The individual layers may have any suitablethicknesses; and in some embodiments may have thicknesses of less thanor equal to about 20 Å, less than or equal to about 12 Å, less than orequal to about 10 Å, etc. It may be advantages to utilize ALD forforming thin layers, such as layers having thicknesses of less than orequal to about 20 Å. In another example embodiment, hafnium aluminumoxide may be formed throughout a switching region by merging hafniumoxide layers and aluminum oxide layers. In another example embodiment, amaterial comprising aluminum, oxygen and silicon (e.g., aluminumsilicate) may be formed throughout a switching region by mergingaluminum oxide layers and silicon dioxide layers.

The portion 52 may comprise any suitable composition, and in someembodiments may comprise one or more of the compositions discussed aboverelative to the portions 20 and 22. Further, although the portion 52 areshown as a continuous layer, in other embodiments the portion to may beformed to comprise less than one complete monolayer; and accordingly maybe formed analogously to the scattered regions 50 of FIGS. 8 and 9.

In some embodiments, an entirety of a switching region may be formed byALD as a single composition having a thickness within a range of fromgreater than 0 Å to less or equal to about 20 Å, or less than or equalto about 12 Å. For instance, FIG. 11 shows a construction 10 eillustrating an example embodiment memory cell having a switching region16 comprising a single ALD-formed composition 54. In some embodiments,such composition may comprise, consist essentially of, or consist of oneor more of GeS, GeSe, SiO, ZrO, TiO, TaO, HfO, AlO, WO, SnO, NbO, ZrTiO,ZrWO, AlTiO, VO, MoO, NiO, YO, ReO, MnO, FeO, SiAlO, SiTiO, etc.; wherethe listed compositions are described in terms of elementalconstituents. In some embodiments, such composition may comprise,consist essentially of, or consist of oxygen in combination with one ormore of aluminum, hafnium, silicon, titanium and zirconium.

An advantage of utilizing ALD to form the entirety of switching region16 is that such may enable the composition and thickness of theswitching region to be tightly controlled. An advantage of keeping theswitching region thin (i.e., within a thickness range of from greaterthan 0 Å to less or equal to about 20 Å, or less than or equal to about12 Å) is that such may enable the PMC to be rapidly responsive tochanging voltage (i.e., may enable high switchability), which may bedesired in some applications.

The various memory cells of FIGS. 1-11 may be representative of a largenumber of memory cells that may be simultaneously fabricated in order toform an integrated circuit memory array.

The memory cells and arrays discussed above may be incorporated intoelectronic systems. Such electronic systems may be used in, for example,memory modules, device drivers, power modules, communication modems,processor modules, and application-specific modules, and may includemultilayer, multichip modules. The electronic systems may be any of abroad range of systems, such as, for example, clocks, televisions, cellphones, personal computers, automobiles, industrial control systems,aircraft, etc.

The particular orientation of the various embodiments in the drawings isfor illustrative purposes only, and the embodiments may be rotatedrelative to the shown orientations in some applications. The descriptionprovided herein, and the claims that follow, pertain to any structuresthat have the described relationships between various features,regardless of whether the structures are in the particular orientationof the drawings, or are rotated relative to such orientation.

The cross-sectional views of the accompanying illustrations only showfeatures within the planes of the cross-sections, and do not showmaterials behind the planes of the cross-sections in order to simplifythe drawings.

When a structure is referred to above as being “on” or “against” anotherstructure, it can be directly on the other structure or interveningstructures may also be present. In contrast, when a structure isreferred to as being “directly on” or “directly against” anotherstructure, there are no intervening structures present. When a structureis referred to as being “connected” or “coupled” to another structure,it can be directly connected or coupled to the other structure, orintervening structures may be present. In contrast, when a structure isreferred to as being “directly connected” or “directly coupled” toanother structure, there are no intervening structures present.

Some embodiments include a method of forming a memory cell. At least aportion of a switching region is atomic layer deposited over a firstelectrode to a thickness within a range of from greater than 0 angstromsto less than or equal to about 20 angstroms. A second electrode isformed over the switching region.

Some embodiments include a method of forming a memory cell. A firstportion of a switching region is formed over a first electrode. A secondportion of the switching region is formed over the first portion, withthe second portion being formed by atomic layer deposition to athickness within a range of from greater than 0 angstroms to less thanor equal to about 20 angstroms. The second portion is a differentcomposition than the first portion. An ion source region is formed overthe switching region. A second electrode is formed over the ion sourceregion.

Some embodiments include a memory cell having a switching region betweena pair of electrodes. The switching region is configured to reversiblyretain a conductive bridge. The memory cell is in a low resistive statewhen the conductive bridge is retained within the switching region andis in a high resistive state when the conductive bridge is not withinthe switching region. The switching region comprises two or morediscrete portions, with one of the portions having a thickness within arange of from greater than 0 angstroms to less than or equal to about 20angstroms and not having a non-oxygen component in common with anycomposition directly against said one of the portions in the highresistive state of the memory cell.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

We claim:
 1. A method of forming a memory cell, comprising: forming afirst portion of a switching region over a first electrode; forming asecond portion of the switching region over the first portion, with thesecond portion being formed by atomic layer deposition to a thicknesswithin a range of from greater than 0 angstroms to less than or equal toabout 20 angstroms; the second portion being a different compositionthan the first portion, one of the first and second portion comprisingone or more members of the group consisting of Ti, Zr and Hf, and theother of the first and second portion comprising Mg; forming an ionsource region over the switching region, the ion source regioncomprising two discrete portions having different compositions relativeto each other, each of the discrete portions comprising one or more ofCu, Si and Al, the ion source region being configured to contribute oneor more of aluminum cations, copper cations and silver cations; andforming a second electrode over the ion source region.
 2. The method ofclaim 1 wherein the switching region has a total thickness within arange of from about 6 angstroms to about 20 angstroms.
 3. The method ofclaim 1 wherein the second portion is formed with at least one atomiclayer deposition cycle and less than or equal to 5 total atomic layerdeposition cycles.
 4. The method of claim 1 wherein the atomic layerdeposition deposits one or more transition metals.
 5. The method ofclaim 1 wherein the atomic layer deposition deposits one or morenon-transition elements; wherein said non-transition elements areselected from the group consisting of metals, semi-metals, alkalineearth elements, and mixtures thereof.
 6. The method of claim 1 wherein:the second portion consists of oxygen in combination with the one ormore members of the group consisting of Ti, Hf and Zr; and the firstportion consists of oxygen in combination with Mg.
 7. The method ofclaim 1 wherein the second portion is at least about 50%, by volume, ofa total thickness of the switching region.
 8. The method of claim 1wherein the second portion is less than about 50%, by volume, of a totalthickness of the switching region.
 9. The method of claim 1 wherein: thesecond portion consists of oxygen in combination with Mg; and the firstportion consists of oxygen in combination with the one or more membersof the group consisting of Zr, Hf and Ti.
 10. The method of claim 1further comprising forming at least one additional portion of theswitching region over the second portion.
 11. The method of claim 1wherein the two discrete portions of the ion source region comprise afirst portion containing an oxide composition and a second portioncontaining a nitride composition.
 12. The method of claim 1 wherein thefirst portion of the ion source region contains CuZrAlTeO and the secondportion of the ion source region contains AlTeN.